In the current optical communication system, laser diodes are used as light sources. After packaging, the laser diode and the package structure is formed as a laser diode element. Referring to FIG. 1, the laser diode element 1 is installed in a metal base 2 by using a fixing glue 3 as a fixing material. A hollow sleeve 4 is combined to the base 2. A hollow ceramic tube 5 is coaxially arranged in the sleeve 4. A cylindrical ceramic cover 6 is coaxially arranged within the ceramic tube 5. A distal end of the cover 6 is ground to have an inclined plane 7 for preventing reflecting light from radiating to the laser diode so that the laser diode is interfered by noises. Furthermore, the cover 6 is coaxially arranged with an optical fiber 8 so that the light radiated from the laser diode element 1 exactly focuses to the core of the optical fiber 8. However, the sleeve 4 can be combined to the joint of the optical fiber. Then the parallel light beams in the optical fiber 8 is guided to the core of another optical fiber at the side of the joint.
Thereby, by above packaging structure, an optical transmitting module is formed. If above said laser diode element 1 is replaced by an optical detector. Then an optical receiving module is formed. However to have a higher coupling efficiency, a longer length is necessary for coupling the light from the laser diode to the optical fiber so as to focus light to the core of an optical fiber. That is to say, the sleeve 4 will make the coupling volume of the laser diode and optical fiber is too larger and much of the light energy is lost in transmission. This is inconvenient in operation. Furthermore, the distance between the light emitting position of the laser diode and the end surface of the optical fiber is too long to be align easily. Moreover, the sleeve 4 is made of ceramic material. Thus, the cost is high.